1. Field of the Invention
The present invention relates in general to a data communications system and pertains, more particularly, to a data communications system that provides for the transfer of data information, control information and signaling information between a telephone system and a computer system. Even more particularly, the present invention relates to a communication control interface apparatus used in such data communication system.
2. Background Discussion
A data communication system of the type described herein may typically include a central processing unit and associated main memory adapted to communicate via a system bus with a communication controller that forms part of a communication subsystem that is adapted to service a number of communication lines. The communication subsystem may typically include a line microprocessor for communicating with the communication lines and a shared memory, and an I/O microprocessor for communicating with the shared memory and the central processing unit and main memory. A system of this type is described in U.S. Pat. No. 4,482,982 and U.S. Pat. No. 4,488,231, both owned by the instant assignee herein.
Reference is also now made herein to U.S. Pat. No. 4,407,014 that describes a communications sub-system employing USART (universal synchronous/asynchronous receiver transmitter) devices for communication between a communications controller and multiple communication lines.
In the above-identified systems, the multi-line controller typically interfaces via USART's with an asynchronous communication line. However, for other forms of data communication, such as with high speed data link control (HDLC) communication, there is a need to then provide a substitute interface area. This interface area is to provide compatible operation between the communication line and the multi-line controller.